1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more specifically to a structure of a semiconductor device having a semiconductor chip fixed on a lead frame, and a method of manufacturing the same.
2. Description of the Background Art
FIG. 11 is a perspective view schematically showing a semiconductor chip to be fixed on a lead frame in a method of manufacturing a conventional semiconductor device. Referring to FIG. 11, conventionally, a semiconductor chip 105 is fixed using a die bonding material 102 on an island portion 101a of a lead frame 101, which has island portion 101a and a lead portion 101b. 
A cross section of a semiconductor device thus manufactured has a structure shown in FIG. 12, after resin sealing. Referring to FIG. 12, semiconductor chip 105 is fixed on island portion 101a by means of die bonding material 102. The bonding pad (not shown) of this semiconductor chip 105 is electrically connected with lead portion 101b using a bonding wire 106. Island portion 101a, die bonding material 102, semiconductor chip 105 and bonding wire 106 are sealed with mold resin 107. Only a plurality of lead portions 101b protrude from mold resin 107 for electrical connection with the outside.
As described above, die bonding material 102 is conventionally used to fix semiconductor chip 105 on lead frame 101. Solder material or adhesive is usually used as die bonding material 102. Usually, solder consisting of Pb (lead)-Sn (tin) alloy is used for this solder material, and lead is thus contained.
Lead intake may cause nerve disorder or disturbance of reproduction system. Moreover, lead may cause anemia or hypertension and is suspected of being a carcinogenic metal. Therefore, if electronic equipment products including solder are disposed of, lead contained in solder may melt into and contaminate soil or underground water to adversely affect human bodies, thus resulting in an environmental problem.
An object of the present invention is to provide a semiconductor device in which a semiconductor chip can be fixed on a lead frame without using a die bonding material, and a method of manufacturing the same. As a result, it becomes possible to provide a semiconductor device capable in which a semiconductor chip can be fixed on a lead frame without using lead (that is, lead-free), and a method of manufacturing the same.
A semiconductor device in accordance with the present invention includes a semiconductor substrate having a main surface, and a semiconductor chip arranged on the main surface of the substrate, wherein a space kept airtight is provided between the main surface of the substrate and the semiconductor chip, and the semiconductor chip is supported on the substrate by making negative the atmospheric pressure in the space relative to the atmospheric pressure outside the semiconductor device.
In the semiconductor device according to the present invention, the semiconductor chip is fixed on the substrate by making negative the atmospheric pressure in the space between the substrate and the semiconductor chip relative to the atmospheric pressure outside the semiconductor device. Accordingly, the semiconductor chip can be fixed on the substrate even without using a die bonding material. This can eliminate the problem of lead contained in solder that is commonly used as a die bonding material.
Preferably, the above-described semiconductor device further includes a seal member arranged between the substrate and the semiconductor chip in order to keep the space airtight.
The space between the semiconductor chip and the substrate can be kept airtight by using the seal member in this way.
In the above-described semiconductor device, it is preferable that a groove for fitting-in the seal member is formed on the main surface of the substrate.
Therefore, it is possible to fit and fix the seal member in the groove.
In the above-described semiconductor device, it is preferable that the substrate is directly in contact with the semiconductor chip, and at least that part of the substrate which is in contact with the semiconductor chip has a mirror surface.
Since that surface of the substrate which is in contact with the semiconductor chip has a mirror surface, the contact parts of the semiconductor chip and the substrate can be tightly connected and the space therebetween can be kept airtight.
In the above-described semiconductor device, it is preferable that a depressed portion to form a part of the space is formed on the main surface of the substrate.
Therefore, the space can easily be formed between the semiconductor chip and the substrate.
A method of manufacturing a semiconductor device according to the present invention includes the following steps.
The semiconductor chip is laid on the substrate in such a temperature environment that is higher than a temperature at a resin sealing step, such that a space kept airtight is created between the substrate and the semiconductor chip. After the semiconductor chip is laid on the substrate, the atmospheric pressure in the space is made negative relative to the external atmospheric pressure by lowering an ambient temperature, so that the semiconductor chip is fixed on the substrate.
In the method of manufacturing the semiconductor device according to the present invention, the semiconductor chip is fixed on the substrate by making negative the atmospheric pressure in the space between the substrate and the semiconductor chip relative to the atmospheric pressure outside the semiconductor device. Therefore, the semiconductor chip can be fixed on the substrate without using a die bonding material. This can eliminate the problem of lead contained in solder commonly used as a die-bonding material.
Furthermore, since the semiconductor chip is fixed on the substrate in such a temperature environment that is higher than a temperature at a resin sealing step, the atmospheric pressure in the space between the semiconductor chip and the substrate can remain negative relative to the external atmospheric pressure, even when heated at a highest temperature at the resin sealing step after the semiconductor chip being laid on the substrate. Therefore, the semiconductor chip remains fixed on the substrate even at the resin sealing step.
In the method of manufacturing the above-described semiconductor device, it is preferable that the step of laying the semiconductor chip on the substrate and the step of supporting the semiconductor chip on the substrate with lowered ambient temperature are performed in a one atmospheric pressure (1 atm) environment.
Accordingly, even in a high temperature environment when the semiconductor chip is laid on the substrate, the pressure in the airtight space can be 1 atm. Therefore, with the subsequent temperature drop, the atmospheric pressure in the airtight space can be decreased to be lower than 1 atm, that is, negative relative to the external atmospheric pressure (1 atm).
In the method of manufacturing the above-described semiconductor device, it is preferable that the 1 atm pressure environment is obtained in a high-temperature chamber of a structure having a portion open to the outside, so that the pressure inside thereof is always kept at 1 atm.
Thus, the 1 atm pressure environment can be created in a high-temperature chamber of a simple structure.
In the method of manufacturing the above-described semiconductor device, it is preferable that the 1 atm pressure environment is obtained in a high-temperature chamber of such a structure that allows variation in its capacity to maintain internal pressure at 1 atm.
Thus, the 1 atm pressure environment can be created in a high-temperature chamber of a simple structure.
In the method of manufacturing the above-described semiconductor device, it is preferable that the step of laying the semiconductor chip on the substrate and the step of fixing the semiconductor chip on the substrate with lowered ambient temperature are performed in a nitrogen gas atmosphere.
This can prevent an adverse effect such as oxidation of the semiconductor chip, the substrate and the seal member.
In the method of manufacturing the above-described semiconductor device, it is preferable that the step of laying the semiconductor chip on the substrate and the step of fixing the semiconductor chip on the substrate with lowered ambient temperature are performed in an inert gas atmosphere.
This can prevent an adverse effect such as oxidation of the semiconductor chip, the substrate and the seal member.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.